1) Field of the Invention
The present invention relates to an apparatus for injecting a solution into a cell. The solution is, for example, a gene solution or a drug solution.
2) Description of the Related Art
Recently, in the field of life science, specifically in the fields of the regenerative medicine and the genome-based drug discovery, by injecting a gene or a drug into a cell, modification of property of the cell is practiced. Such a technology enables to elucidate a function of a gene, and also enables a tailor-made medicine for providing a care suitable for a genetic characteristic of an each individual.
To produce such cells, various solution injecting technologies have been proposed. Specifically, there are a biological method such as a virus vector method, a chemical method such as a lypofection method, an electric method such as an electroporation method, a physical method such as a particle gun method, an optical method such as a laser injection method, and a mechanical method such as a microinjection method.
The virus vector method is a method for gene transfer to a cell in which a genetically modified virus is produced, and by the infection mechanism of the genetically modified virus, the gene transfer is carried out. The lypofection method is a method in which an electrically charged liposome and a DNA are combined, and by making it adsorb on the surface of a cell, the DNA is transferred into the cell. However, such biological method and the chemical method have disadvantages. There is a great limitation on combinations of a cell and a transfer substance in these methods. Especially, the virus vector method has a disadvantage in which danger of causing infectious diseases is relatively high because a cell that has strong infectivity is used.
The electroporation method is a method in which a gene solution or a drug solution is injected through a hole of a cell membrane that is formed by rupturing the cell membrane with an electric pulse. The particle gun method is a method for the gene transfer in which a cell membrane is ruptured by shooting a cell with the minute particle to which a gene is adhered to transfer the gene into the cell. Although the electric method and the physical method have an advantage in which combinations of the cell and the transfer substance are not limited, these methods also have a problem in which success rate of the gene transfer stays low at several percent because control of an apparatus is difficult, and there are cases in which the cell membrane cannot be properly ruptured, or the cell membrane is ruptured too much resulting death of the cell.
On the other hand, the optical method such as the laser injection method and the mechanical method such as the microinjection method have been receiving attention because these methods have high success rate and they are safe.
In the laser injection method, a drug solution is dissolved in a cultivation solution of the cell, and an opening is formed in a cell membrane of the cell by irradiating a laser. The drug solution seeps into the cell by the Brownian movement (refer, for example, to the patent literature 1). This method has an advantage in which the solution injection according to a microscopic structure of the cell is possible because the cell membrane is ruptured by the laser.
In the microinjection method, a drug solution is filled in a thin needle that has a diameter of 1 micrometer (μm) or less, and by injecting the needle into a cell, the drug solution is injected into the cell (refer, for example, to the patent literature 2). In this method, the needle tip can be controlled to minimize damage to the cell by carrying out the injection under a microscope by a skilled operator, and with a control device that has high resolution. Therefore, nearly 100% success rate can be obtained. This method also has an advantage in which this method does not limit a combination of the cell and the transfer substance.                Patent Literature 1: Japanese Patent Application Laid-Open No. 2003-70468        Patent Literature 2: Japanese Patent Application Laid-Open No. H8-290377        
However, the laser injection method limits concentration and kind of the drug solution because the Brownian movement is used as a prime mover for the drug solution to seep into the cell. Moreover, the use of the Brownian movement as the prime mover leads to a low introducing efficiency in introducing the drug solution because directions of movement of drug molecules are irregular. Therefore, a large amount of the drug solution, which is expensive, is necessary, and the injection by this method costs a lot.
In the microinjection method, when a same needle is repeatedly used, a part of the cell membrane sticks to the needle. As a result, the tip of the needle becomes thick, and the needle becomes unusable. Moreover, to pierce through the cell membrane with the needle, the needle has to be injected keeping some amount of momentum. Therefore, it is impossible to carry out the injection according to the microscopic structure of the cell. For example, cytoplasm of a suspended cell has thickness of only 1 μm to 2 μm, therefore, it is difficult to set the tip of the needle on this part to carry out the injection.